Chemical Symbols and Chemical Symbols and formulasformulas

What do we need to know in order What do we need to know in order to write formulas?to write formulas?

What do we need to know in order What do we need to know in order to correctly name compounds?to correctly name compounds?

Chemical Symbols and formulas

Elements are represented by SYMBOLSSYMBOLS:

NaNa FF

CuCu

Compounds are represented by FORMULAS:FORMULAS:

NaClNaCl CuSOCuSO44

Al(NOAl(NO33))33

Chemical Symbols and formulas

Chemists combine element symbols into chemical formulas to represent compounds (two or more elements combined)

NaNaClCl

AlAl POPO44

Polyatomic Polyatomic ion!!ion!!

(in CRM)(in CRM)

Chemical Symbols and formulas

A formula shows two things:

The kinds of elementskinds of elements in the compound ANDThe number of elementsnumber of elements in the compound!

NaNa

1 sodium atom

CCll1 chlorine atom

AlAl POPO44

1 aluminum atom

1 phosphorus atom

4 oxygen atoms!

More information about those little numbers in the formulas….

Chemical Symbols and formulas

AlAl POPO44

When only one atom of an element is present, no number is used.

SUBSCRIPTSUBSCRIPT

If more than one atom of an element is present, we state how many.

Chemical Symbols and formulas

How many atomsatoms are present in these compounds?

CuCuSOSO44 1 Copper,1 Copper, 1 sulfur, 4 oxygen1 sulfur, 4 oxygen

HHFF 1 hydrogen,1 hydrogen, 1 fluorine1 fluorine

NHNH44ClCl 1 nitrogen, 4 hydrogen,1 nitrogen, 4 hydrogen, 1 1 chlorinechlorine

Chemical Symbols and formulas

Is that all there is to it?

NOPE.NOPE.

MgMg(NO(NO33))221 magnesium……1 magnesium……

2 nitrogen……2 nitrogen……

6 6 oxygen!!oxygen!!

There are TWO nitrateTWO nitrate ionsions here.

(NO(NO33)) is the polyatomic ion ‘nitratenitrate’ remember!

Everything INSIDE the parenthesis must be multiplied by the number OUTSIDE the parenthesis.

Chemical Symbols and formulas

In order to write formulas and correctly name compounds we need to know something about

Periodic tablePeriodic table

ElectronsElectronsAnd the

Chemical Symbols and formulasAtoms and their electrons

I NEED 8 I NEED 8 electrons in my electrons in my outer shell!outer shell!

All atoms wish to have 8 8 electronselectrons in their outerouter

shellsshells.

These are called valence valence electronselectronsThey are willing to loselose

or gaingain electrons to achieve this number!

Called the Octet Rule!

Ions• An ion is an atom or group of atoms

that has a charge • A compound that is composed of ions is

called an ionic compound.• Ionic compounds usually form between

a metal (cation) and a nonmetal (anion). (Look at Periodic Table)

• They may also form between a polyatomic ion (like ammonium) and either a metal or nonmetal.

• In ionic compounds, you will TRANSFER valence electrons

Ions• A cation

– positive ion – formed when an atom loses electrons.

• Example: Na+

• An anion– negative ion– is formed when an atom gains electrons

• Example: Cl-

• A monatomic ion is one element with a charge

• A polyatomic ion is more than one element with a charge

• Example: SO42-

Chemical Symbols and formulas

+1

+2 +3+4 -4 -3 -2 -1

0

Cations

(metals)

Anions

(non-metals)

Chemical Symbols and formulasThis losing and gaining of electrons is

why certain elements combine the way they do. (Opposite charges attract)

Even though ions have charges, cations and anions must combine in a way that cancels out their + and - charges.

Na + Cl-e-

Here, have my electron!

Why thanks, don’t mind if I do!

e-

Chemical Symbols and formulas

Na+

Cl-

And so they combined to live happily ever after….

Na LOST, Cl GAINED, and the compound is neutral

(which means that all plusses and minuses cancelled!)

I don’t need this old plus anymore!

I don’t need this old minus anymore!

Writing Ionic Compounds

1. Find cation (metal) and write symbol and charge2. Find anion (nonmetal) and write symbol and charge-If ends in “ide” on periodic table-If end in “ate” on class copy sheet3. Criss Cross from top to bottom4. Charges cancel (remove + & -)5. Simplify/reduce if possible

*Don’t forget parentheses when you bring down *Don’t forget parentheses when you bring down anything other than a 1 with polyatomic ions.anything other than a 1 with polyatomic ions.

*For transition elements with varying charge, the *For transition elements with varying charge, the roman numeral indicates the charge on the metal.roman numeral indicates the charge on the metal.

Formula for boron oxide

1.Find cation (metal) and write symbol and charge.

B3+

Formula for boron oxide2. Find anion (nonmetal) and write symbol and charge. Since it ends in “–ide” it is on the periodic table.

B3+ O2-

Formula for boron oxide

3. Crisscross the superscripts so they become subscripts.

B3+ O2-

Formula for boron oxide

4. Remove charges (+ and – cancel) 5. Reduce subscripts when possible.

(not possible here)

B2O3

Examples

1. Sodium & Chloride2. Magnesium & Bromide3. Calcium & Sulfide4. Sodium & Nitrate5. Ammonium and Sulfate

Naming Ionic Compounds (Regular & Polyatomic)

1. Write the name of the cation (metal)2. Write the name if the anion (nonmetal)-If only 2 elements, cut off the ending of

the 2nd element and add “ide”-If a polyatomic ion, use the name the

class copy data sheet gives you.

Examples

1. NaCl2. MgSO4

3. K3PO4

4. Ca(ClO3)2

5. NH4NO2

• Sodium chloride• Magnesium sulfate• Potassium phosphate• Calcium chlorate• Ammonium nitrite

Naming Ionic Compounds (Variable Charge)

1. Check to see that these metal are in the d-block and have a variable charge

2. Write the name of the cation (metal) with (roman numerals)

3. Write the name of the anion (nonmetal or polyatomic ion)

4. Add 1’s to elements with no #’s5. Reverse criss cross and add positive charge to the

metal and a negative charge to the nonmetal6. Check the charge on nonmetal-If incorrect multiply both sides-# attached to the metal goes in the roman numeral

More examples

• Lead (IV) Oxide• Iron (II) sulfate• Cobalt (II) chloride• Copper (II) phosphate• Zinc chloride

• PbO2

• FeSO4

• CoCl2• Cu3(PO4)2

• ZnCl2